Jillian Michaels, the hard-core personal trainer from NBC's The Biggest Loser, spent her adolescence overweight and unhappy. Enrolling in a martial arts class helped her shed the pounds and inspired her to dedicate her life to helping others lose weight. In her new book, Master Your Metabolism, she writes that the key to weight loss is balancing your hormones. As season seven of the show comes to an end this week, Michaels talks to TIME about why she recently called The Biggest Loser contestants "half dead," how much exercise the average person really needs and what changes you can make in your life to lose ten, twenty or hundreds of pounds. (See pictures of what makes you eat more food.)

Tell us about the three diet secrets from your new book.
People tend to think that metabolism is genetically predetermined. That you're either cursed or you're blessed. And that's not true. You can dramatically affect the expression of your metabolism and your biochemistry by the way you eat and the way you live. So, the first part of the plan is to remove all of the chemicals in your environment  your cleaning supplies, your beauty supplies and your food supply. The second part is to restore power nutrients to your diet. The third part is to make some easy changes to rebalance your life, everything from getting enough sleep, to working out correctly, to what time of the day you should work out, to how much you should be eating.

You were overweight as a teenager. Does this make you more sympathetic to the contestants on The Biggest Loser?
I'm not sympathetic. I have zero sympathy. I understand about emotional eating, I understand how painful the process can be, but I also understand that change is possible. In my experience, honesty is the best policy. And being a friend to somebody is not always the best way to help them. (See nine kid foods to avoid.)

Contestants train for at least four hours a day on Biggest Loser. In real life, it's not usually possible for someone to get out and exercise for four or five hours a day.
Not only is it not possible, it's not safe. You only want to work out like that when you're being medically supervised. We have doctors who have to approve everything I do. I also have a nutritionist and a dietician. And the people who come to the show are very sick! They are 400 pounds! It's very different when you have less than 50 pounds to lose.

So how much should people exercise when they only have less than 50 pounds to lose?
The key is intensity. Incorporate weight training, but don't overdo it. Don't do more than eight hours a week. Definitely not more than ten hours a week.

You recently said that by the time The Biggest Loser contestants come to you they're half dead. What did you mean by that?
Yes, I said "half-dead" And everybody was like, "oh, I can't believe she said that." Are people just not tuning into the show? We've got 30-year-olds whose internal organs are 60. If we were having this conversation about somebody who was a drug addict or somebody who had anorexia or bulimia, we would openly admit that it was suicide.

So what do you think is the number one worst thing people are doing to their bodies right now?
Oh my God, they eat processed food and it is horrifying to me! You look at people, they'll be having a sandwich on white bread with turkey. Okay, well, the turkey's probably processed, meaning it's got nitrates in it. And of course white bread doesn't grow white. It's stripped of all its nutrients and all its fiber. High fructose corn syrup: poison. Artificial sweeteners: poison. Artificial coloring: poison. MSG: poison. Nitrates: poison. Unload all those things and you're off to a good start. (See the truth about 10 dieting myths.)

You are so busy, so how do you stay fit?
I'm not going to lie, it's really hard. When you don't have time to work out, you have to be really meticulous about your diet. And when you do have time to work out, make it count. Yesterday I ran five miles and went to a yoga class.

So you are doing double exercise.
Well, this is something that I do. Not realistic for the average person. I'll run in the morning and then I'll do my resistance training at night. On days like today when I can't get it in, I know that I did two yesterday.

Seems like a good way of losing weight  if you can do it.
If you can do it. I think most people can't, and I can understand why. Just do what you can, but when I say that, I don't mean just take the stairs. When I say "do what you can," I want half an hour, five times a week. "Do what you can!" Walk your lunch hour. Do a video in your living room for thirty minutes.

I've heard that you are really into motorcycles. What kind of motorcycle do you have?
I have five. And I'm emotionally attached to all of them, so I can't let one of them go. I have a KTM 990 Superduke, I have a Ducati 848, I have a Ducati Desmosedici, I have a Yamaha SZ1000 and I have a Harley.

There are only a few hundred Desmosedicis in the world, right?
Only 500 in the United States, and I'm the only woman in the world that has that bike. And of course my ego is so happy [about that] I can barely stand it.